1. Field of the Invention
The present invention relates to a CPP (Current Perpendicular-to-the-Plane) type magnetic head, a head suspension assembly on which this magnetic head is mounted, and a magnetic reproduction apparatus.
2. Description of the Related Art
In recent years, sizes of magnetic recording apparatuses such as hard disk drives have been rapidly reduced, and recording densities have been increased. This tendency is expected to rise further. With the increase of the recording density, there is a demand for a highly sensitive sensor, and a current perpendicular to plane-GMR (CPP-GMR) element has been developed to meet this demand. By use of the CPP-GMR element, a magnetic head having high density and output can be formed.
This type of magnetic head comprises a pair of shielding layers which define a gap length, and a current supply layer (lead layer) which conducts a sense current to the CPP-GMR element. Usually, the shielding layer is formed outside the lead layer. That is, the CPP-GMR element is held between two upper and lower lead layers, and this state is held further by two shielding layers. To increase the recording density further, it is proposed that the shielding layer be also provided with a function of the lead layer (see, e.g., Jpn. Pat. Appln. KOKAI Publication No. 2002-314165). It is proposed that the lead layer is connected to the shielding layer on the other side of medium facing surface in order to shorten the gap length and enhance the recording density (see, e.g., Jpn. Pat. Appln. KOKAI Publication No. 2002-25016). In this constitution, the sense current flows through the shielding layer until the current flows through the CPP-GMR element.
Additionally, the magnetic head reads information by use of an element resistance which changes with the magnetic flux from the recording medium. However, when the sense current flows through the shielding layer, the resistance is generated even in the shielding layer. Since the shielding layer has weak magnetoresistance effects, the signal-to-noise ratio of a reproduced output is accordingly degraded. Since a tunnel magneto-resistive (TMR) element has a large element resistance, an influence of a resistance change by the shielding layer is not very conspicuous. On the other hand, since the resistance of the CPP-GMR element is very small, and a ratio of the resistance change of the shielding layer is large, noise components are easily superimposed on an output by a disturbance magnetic field. This is remarkable especially in a case where a magnetic shielding film is also used as a lead film as in a technique described in the Jpn. Pat. Appln. KOKAI Publication No. 2002-25016, and there is a demand for a certain countermeasure.